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I'm working with a legacy schema which has 3 particular tables backing a single class, listed below:

  • table_1_month
    • # All items that are < 1 month old.
  • table_1_year
    • # All items that are between 1 month and 1 year old.
  • table
    • # All items that are older than 1 year.

All 3 tables have the same schemas, but the only difference between them is that the time it was last updated determines which table the rows exist in.

I know Datamapper has the ability to specify different storage_names via the following syntax:

class Klass
  storage_name[:default] = "table"
  storage_name[:onemonth] = "table_1_month"
  storage_name[:oneyear] = "table_1_year"
end

How would I write a query that specifies the repository by which an article is accessed? (For example, the query to access all rows that are 2 months old would require retrieving and appending all rows from table_1_month to a subset of the rows in table_1_year)

alexhuang91
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1 Answers1

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The easiest way that I was able to get something along the lines of what I wanted was to add new repositories.

Datamapper.setup(:default), <Insert database connection url>
DataMapper.setup(:onemonth), <Insert the same database url>
Datamapper.setup(:oneyear), <Insert the same database url>

In the model class,

class Klass
  storage_name[:default] = "table"
  storage_name[:onemonth] = "table_1_month"
  storage_name[:oneyear] = "table_1_year"

  # Psuedocode
  def get_from_timeperiod(start_time, end_time)
    time_one_year_ago = <some other int>
    time_one_month_ago = <some int>
    if end_time < time_one_month_ago
      DataMapper.repository(:onemonth) { self.all( self.updated => (start_time..end_time) ) }
    elif end_time < time_one_year_ago
      DataMapper.repository(:oneyear) { self.all( self.updated => (start_time..end_time) ) }
    else
      self.all( self.updated => (start_time..end_time) )
    end
  end
end

(Update 10/31 6:13pm) The other alternative that I found is to use a direct database query instead of the DataMapper.repository(:onemonth) { } which results to struct objects:

 repository(:default).adapter.select("SELECT * FROM table_one_month WHERE updated between #{start_time} and #{end_time}")

I personally find that the first way is a lot cleaner.

Please let me know if there's anything better that I can do!

alexhuang91
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  • 1
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